Synthetic felts



Dec. 18, 1956 H. A. sEcRlsT 2,774,129

A SYNTHETIC FELTS Filed Nov. 6, 195o IN VEN TOR.

United States Patent SYNTHETIC FELTS Horace A. Secrist, Dedham, Mass., assgnor to The Kendl-.ll Company, Boston, Mass., a corporation of Massac usetts Application November 6, 1950, Serial No. 194,384

1 Claim. (Cl. 28-79) This invention relates to conformable, pliable, extensible felt-like materials composed primarily of synthetic bers.

Hitherto many non-woven fabrics and sheet materials have been manufactured by assembling synthetic bers in the form of loosely associated brous webs and stabilizing the ber congurations by developing the coalescent properties of the synthetic bers iny some cases, and in others by adding adhesive bonding agents in the form of liquids, powders or potentially adhesive bers. 'Ihese non-woven materials however, have depended almost entirely on the positive adhesive bonding between the bers for their integrity since the surfaces of the commercially available synthetic bers are generally smooth and the bers themselves essentially straight, precluding the surface frictional action and capacity for entaglement which is thought to provide the integrity in natural felts such as wool. As a result, these products lack exibility and have extensibilities essentially the same as those of the cementitious substances us'ed to hold them together. Further, even though such prior art materials have sometimesA been characterized as felts, they lack the bulk or thickness per unit weight, and the resilence and intimacy of ber association of true felts.v

For the rst time in the art, to my knowledge, I have found it possible to provide true felts which can be composed entirely of synthetic bers. By true felts I refer to nonwoven brous materials in Whilch the bers are held together by frictional interlocking and entanglement by .virtue of articially-induced kinks, bends, twists and curls in the bers. Even though it may be desirable for some purposes to strengthen my synthetic felts by providing additional coherence in the form of adhesive bonds between and among the bers, the basic felt-like properties of my materials are derived from the frictional interlocking and entanglement of the bers independent of added or self-generated binder substances.

The synthetic felts of my invention are adapted to many of the uses for which wool felts are commonly employed as well as a wide variety of other uses depending on the chemical and physical properties of the synthetic ber component. For instance, felts composed of .bers of regenerated cellulose are characterized by a softness, pliability, porosity, and absorbency that make them particularly well suited for use in the medical v,and-surgical yelds as bandages,.sponges, dressings and the like. The network of interlocking bers closely simulates the structural arrangement of the bers of natural leather providing a base material combining substantial tensile strength, exibility, and conformability which can be readily saturated, impregnated, and nished into articles strikingly similarto natural leather in physical properties as Well l rice 2 ity of my felts coupled with the tendency of the bers to readjust to new congurations of entanglement when the original structure has been alteredby deformation stresses enables them to be molded without rupture to many deep-drawn complicated shapes.

Among the many other applications for my novel products are battery separators, industrial lters, wiping clothes, pillow and mattress stuing, and the like.

These and other characteristics of my invention will be more readily appreciated from the following description of an embodiment thereof selected for the purposes of illustration and shown in the accompanying drawings, in which:

Figure 1 is a plan view of a section of fabric in accordance with my invention.

Figure 2 is a cross section along line 2 2 of Figure l.

To prepare my synthetic felts I'ultilize synthetic bers having latent, substantial, built-in potential energy of a curl-inducing nature, hereinafter abbreviated as B. I. P. E. I assemble these bers into a loosely associated brous sheet or body either by means of conventional textile machinery such as cards or garnets, by pneumatically distributing the bers on a suitable supporting medium, or otherwise. I then subject the assembled brous body or sheet to the action of an energy-releasing agency, whereby the bers Writhe, gyrate, curl, loop, twist and bend, condensing and contracting the brous body as they entangle and interlock to form a synthetic felt as shown in Figures 1 and 2. On removal of the activating medium the bers 10 of my felts are in a network or stable conguration of intermeshing random kinks, gyrations, bends, twists, writhes, and curls as shown in the drawings, such that the felt attains a high degree of resistance to forces tending to interrupt its continuity or structural coherence or to deform itfrom its contracted condition.

The pronounced B. I. P. E. of the synthetic bers which is a pre-requisite to the practice of my invention may take various forms. It may exist incertain bers commercially available because of non-homogeneity of composition, physical asymmetry or instability, or differential stresses implanted in the process of manufacture, or may be induced at a later stage by physical or chemical treatment. Whether inherent or induced in my synthetic bers, the B. I. P. E. represents a form of stored or potential energy which can be released by appropriate thermal and/ or chemical means to cause the bers to gyrate, writhe, squirm, twist, bend, shortening in span, and in some cases in length. Because of the preparatory association -of the bers this motion is not wasted but results in an intercurling, interlocking and felting of the bers. Whatever may be the exact explanation of the writhingvand twisting of the bers during their treatment to produce a felting action, such action cornes as the result of what I have herein termed the -built-in potential energy (B. I. P. E.), and this B. I. P. E. may be present in certain commercial bers as hereinbefore -referred to or may be v produced in bers during or after their manufacture as herein set forth.

Thermal creation of diierential stresses within certain special bers is one method of obtaining-.the built-in potential energy referred to above. For example, in the manufacture of certain calendered polyethylene sheet materials, the calender rolls are maintained at Widely separated temperatures. It is believed that differential stresses and/ or greatly varying crystalline conditions and arrangements lare thus induced. Atany rate, when monolaments are cut from such polyethylene sheets, chopped into appropriate lengths 01A", for instance), assembled in the form of a brous web, and subjected to temperatures of the order of 240 F., the stored energy is released and the bers go through their felting motions. Slightly l "higher temperatures may be i to setthe twist inithe Vinylite. v.rod were removed from the water and cooled. .Themonoj container.

employed if it is desired to produce some spot welding or fusion of the bers to'each other in addition to lthe ,felting action. Alternatively, a liber-forming` substance maybe extruded or pulled-.through au orifice. .the circunlferential .temp erature's Y of-which` are u non-uniform, orotherwise in which-the oriceproduces unequal drafting eect. upon the ber, or inwhichradial asymmetry of structure is .induced n-the ben. Inthese ways,..for..illustration, a berxmay be produced lwhich under appropriate .energy releasing agencies will curl and twist. l

. Mechanically-induced. B. I. 13..l E. is further illustrated by the following` example. A -monolament of Vinylite (aco-polymer vof .vinylv chloride andV VinylA acetate*v com- .mercially distributed.-by;the Carbide andCarbon Company) was tightly twisted under tension and wound around a .glass rod to prevent kinking. f The rod Vwith themonolament wrapped around ite-was immersed inboiling-water The `monolament and lament was unwound from the glass rod, cut into lconvenieut-ber lengths,y and these lengths lrandomly distrib- -uted in a small container in :suicient quantity to ll. the 'The container. land intermingled ybers were -then placed in anoven maintained at approximately 230 F. (anytempe'rature above-the boiling'point of watenand Vbelow the melting pointV of the bers would be operative),

whereupon the potential energy=was released andztheiplastic memories of the bers .came into play so `thatthey .f strove to reassume their .originaluntwisted `forms,:.writh ung, contortmg, interloopingandzfelting in the process.

`B. I.P. 'En may alsoexist in synthetic bers as a result of nonhomogeneous composition. 'For. example, "in the ."spmulng of bers of regenerated cellulose, differentsolu- `.tions orspinning dopes'may bei fed into a singleI spinneret atto prod uce a ber'ofnonhomogeneous compositionand properties. As a result, when such bers are subjected to appropriate.V swelling agents,- such as caustic alkali," the two ber constituents swell and/or contract to a different degree causing randornrcurling, interkinking ofthe bers suiclent tofelt them when they are so treated in the form of an associated brous body or sheet.

V` A commercially available ber with B. I. P. B.is Fiber E `(aA regenerated cellulose ber manufactured by the'E. I. du Pont de lNemours Company). I have producedsatisfactory'felts' from this ber by the following techniques:

Example I Sixdenier'Fiber E lamentsf were cut into convenient ber lengths and worked into the forml of 'a brous sheet -weighing 70 grams pei-square yardron a carding machine. lThe sheet was given alight press between nip lrollsj'arld oated in a bath of20%V NaOH vat23" C., for a periodof about 120 seconds. The 'treated sheet was removed-from fthe caustic, washedwith watercontaining 10% NaCl,

washed with plain water,-neutr'a1ized with dilute-acetic acid, 'again washed with water andl dried on a steam can.

An=area contractionY of 48.7%, based on the original `dimensions of the untreated sheet, was observed.' The product was soft and pliant tothe touch and'had a-felt-like appearance. Y '.:Examplel inExample 1 Yresulting in; an 'essentially j similar product. Example 3y Aiibrous' sheet-'waslpreparediandi treated Aas'irrlxaln- 70 547,288

-The dried product wasA felt-likeV in appearance and prop- .berg rayon, thermoplastic bers',-both-lcellulosic and non#y ple 2, except that the sodium chloride wash was omitted.

erties and in addition had a pebbly texture suggesting particular utility as a base material for the manufacture of leather-like products.

The synthetic bers of my novel felt-like materials may be composed of any ber-forming substance whichis capable of beingY-spunf'extruded, cut or otherwise fash-v ioned into Icontinuous filaments. Applicable bers include :those 'olil regeneratedcellulose: such as.` viscose and...Be'm

cellulosic, examples of which are: cellulose acetate,*cellu` losegpropionate, cellulose ;:.-butyrate,.'ethylv cellulose and Fibers made of mixed esters such as benzyl cellulose.

cellulose acetate-propionate also'are useful. Others of an entirely diierent chemical nature, however, may be employed, suchl as those made of vinyl polymers, for example, polyvinyl chloride, polyvinyl acetate, polyvinylidenechl'o'rideg' or vinylcopolyiners, and' those 4of the polymercially known as nylon.

' family are also-useful.

l during 4*their* manufacture or thereafter when the ber lI= havechosen synthetic bers'as theA raw materialsffor 'my felts becausethe B. I: necessary for the practice i. of my inventioncan be conveniently induced in 'the bers substances are in 'easily vhandled continuous lamentform. Accordingtothe, general principles of my invention it is v'possible to'producea vsinrilar B. I. P.- E; in natural bers and 'to release the energy stored thereby'iwhen the` bers have beenV assembled inA the formrof associatedv brous sheets. 1. Howevenjthejlimited lengthsI of :natural'bers andgthe `practical difficulty of inducing dierential-stresses :and thelike. in them-make the'practicei of vmy invention with naturalk berscommercially inexpedient'except as lthey may be combined'with'synthetic materials to Vproduce laminated bers or the llike havingB.I. P. E.

'Although it is essential that synthetic bers having ;.B. I. PIE.' be employed in major .proportion inthe prepaf 40 ration of my products, natural bers or'syntheticjbers without this special energy may be utilized and combined therewith in minor proportions.

' I claim:

.A nonwoveniabric sheetcomposed essentially of un.` spunrsynthetic-bers held. in a network relationship -by f l the :release'of lbuilt-in lpotential energy of. a curl and twist .inducing nature, which .results in'4 bers having artificially .induced bends,' twists, curls, writhes and` gyxrationsV `which Yfrictionally ,interlock to form a coherent fabricV sheetl structure `:which vis primarily kdependent for Aits Vintegrity ...upon saidintenlock of saidbers.

.fneferencescifed in' theme of. this parent Fone-1cm PATENTS `Great Britain Augy 21; 1942 amide type, anpimportant example of which is that com-V Fibers of thepolyacrylate g 

